The present invention relates to a double-headed mass sensor for determining a minute mass of a nanogram (10xe2x88x929g) order, for example, a mass sensor for sensing microorganisms such as bacteria, viruses, and protozoa or the like (immune sensor), and a mass sensor for sensing moisture, toxic substances, or specific chemical substances such as taste components (moisture meter, gas sensor, and taste sensor), and a method for sensing a mass.
In the present invention, two diaphragms used look like and function as xe2x80x9ctwo headsxe2x80x9d, the mass sensor of the present invention has been named a double-headed mass sensor.
The double-headed mass sensor of the present invention can sense change in the mass of a diaphragm by measuring a change in resonant frequencies caused by attaching a specific material on a diaphragm, and it is possible to sense change in resonance frequency due to change in the mass of the diaphragm itself; and therefore, the mass sensor can also be used as a thickness meter for vapor-deposited films or a dew indicator.
Furthermore, even if the mass of the diaphragm is not changed, the double-headed mass sensor of the present invention can also be used as a vacuum gauge, a viscosity meter, or a temperature sensor by placing it in an environment to cause change in resonant frequency, that is, by placing it in a medium environment of gases or liquids having different degree of vacuum, viscosity, or temperature.
Thus, although the double-headed mass sensor of the present invention can be used in various applications depending on its embodiments, the same basic principle is applied to the measurement of change in resonant frequencies of the diaphragm and the resonating portion including the diaphragm.
The double-headed mass sensor will be described below focusing on the case where it is used as an immunosensor.
Among what are referred to as diseases, microbiological examinations are recently essential for the treatment of diseases caused by microorganisms such as bacteria, viruses, or protozoa, to find their pathogens, to clarify their types, and to determine drugs to which they are sensitive.
At present, in the first stage of the microbiological examinations, since the cause of a disease and the type of the pathogen can be estimated from the symptoms, various specimens are selected depending on the type of the disease, pathogens present in the specimens are morphologically identified, or antigens or specific metabolites of pathogens (e.g., toxins or enzymes) existing in the specimens are immunochemically identified. Such processes include smeartests, staining, or microscopy used in bacterioscopy, and in recent years, instantaneous identification has become possible in this stage by fluorescent antibody staining or enzymatic antibody staining.
Also, the virus serological test, used in the detection of viruses, is a method for proving the presence of specific immune bodies (antibodies) that appear in the serum of a patient. For example, a complement fixation reaction is used in which the presence of antibodies or antigens is determined by adding complements to test blood, and by observing whether the complements react with antigens or antibodies in the blood and fix to the cell membranes of the antigens or antibodies, or destroy the cell membranes.
In the treatment of diseases caused by microorganisms or the like, as described above, adequate treatment can be conducted by finding pathogens in an early stage through the microbiological examinations described above, and the patient can be led to recovery without worsening of the condition of a disease.
However, with methods such as smeartests, staining, and microscopy, the detection of microorganisms is often difficult depending on their quantities, and time-consuming treatment such as the culture of specimens on an agar medium must be conducted as required. Also in the virus serological test, since measurements must usually be performed during both the acute stage and the convalescent stage for determination from the changes in the quantities of antibodies, there is the problem of time consumption from the point of view of prompt diagnosis.
Therefore, as seen in complement fixation reactions described above, when a substance to be sensed reacts with a catching substance which catches the substance to be sensed by reacting only with a specific substance to be sensed, microorganisms, the mass of the catching substance increases by the mass of the substance to be sensed, even slightly, and considering such a fact, the detection of pathogens is considered to be possible by the measurement of such a change in the mass. Such an increase in the mass similarly occurs in the relationship between a catching substance and a chemical substance such as a specific gaseous substance and a smell component, and also applies to the case where a substrate itself without change in the mass is a catching substance, on which a specific substance is deposited or added. On the contrary, when a reaction in which a substance to be sensed caught by a catching substance or the like is released, the mass of the catching substance or the like slightly decreases.
As an example of a method for sensing change in such a small mass, U.S. Pat. No. 4,789,804 discloses in FIG. 22 thereof a mass sensor 80 comprising a quartz oscillator 81 and electrodes 82, 83 facing the quartz oscillator 81. When any substance adheres externally on these electrodes 82, 83, the mass sensor 80 senses change in mass using change in the resonant frequency of the thickness slip oscillation (shear mode) of the quartz oscillator 81 in the direction of the surface of the electrodes. Since such a mass sensor 80 measures change in resonant frequency basically caused by change in the mass load on the quartz oscillator 81, such a mass sensor 80 is considered to be able to be used also as a thickness meter for measuring the thickness or the growth of a vapor-deposited film, or a moisture meter.
However, when such a quartz oscillator 81 is used, since the part on which an external substance adheres and the part for detecting resonant frequency are in the same location, for example, the resonant frequency becomes unstable because piezoelectric properties of the quartz oscillator 81 itself vary due to the temperature of the specimen or change in temperature. Also, if the specimen is a conductive solution, when the mass sensor 80 is immersed unprotected in the specimen, a short-circuit between electrodes 82, 83 may occur. Therefore, the mass sensor 80 must always be subjected to insulation such as resin coating.
Furthermore, various vibratory gyro sensors are disclosed in International Patent Application JP97/01094 in accordance with the Patent Cooperation Treaty, and their structures resemble the double-headed mass sensor of the present invention described below in appearance. Differences between such vibratory gyro sensor and the double-headed mass sensor of the present invention will be compared in the description of the embodiments of the double-headed mass sensor of the present invention.
The present invention aims to improve the properties of the mass sensor as described above.
According to the present invention, there is provided as a first double-headed mass sensor, a double-headed mass sensor characterized in that between a first connecting plate joined to a first diaphragm at respective sides and a second connecting plate joined to a second diaphragm at respective sides, a resonating portion comprising the first connecting plate, the second connecting plate, the first diaphragm, the second diaphragm, and a first sensing plate, and a main element being provided on at least one plane surface of the first sensing plate, bridged in the direction perpendicular to the joining direction of each of said connecting plates and each of said diaphragms, is joined to a sensor substrate at at least a part of sides of said first connecting plate and said second connecting plate.
Here, the main element is preferably split in the direction perpendicular to the joining direction of the first sensing plates and each of the connecting plates.
A part of sides of the first connecting plate joined to the sensor substrate means more specifically the sides of the first connecting plate is a face that opposites to the joining surface with the first diaphragm, and this is the same for the second connecting plate. That is, the diaphragms are joined to the sensor substrate via respective connecting plates. Such a mode of joining between each of the connecting plates and the sensor substrate is common to the double-headed mass sensor of the present invention to be described below. Also in the first double-headed mass sensor, the first sensing plate may be joined to the sensor substrate, or, a gap may be provided between the first sensing plate and the sensor substrate. Such a mode of providing the first sensing plate is similarly applied to every sensing plate in other double-headed mass sensors described below.
Also according to the present invention, there is provided as a second double-headed mass sensor, a double-headed mass sensor characterized in that a first connecting plate is joined to a first diaphragm and a second connecting plate is joined to a second diaphragm at respective sides, said first connecting plate is positioned between a first sensing plate and a second sensing plate, said second connecting plate is positioned between said first sensing plate and a third sensing plate, so that the respective sides are joined to each other, and a resonating portion comprising the first connecting plate, the first diaphragm, the second connecting plate, the second diaphragm, the first sensing plate, the second sensing plate, the third sensing plate, a main element provided on a part of at least one plane surface of said first sensing plate, and/or a subsidiary element provided on at least a part of the plane surface of at least one of said second sensing plate and said third sensing plate, is joined to a sensor substrate at at least a part of sides of said respective connecting plates.
Here, the main element and/or subsidiary element may be split in the direction perpendicular to the joining direction of each of the sensing plates and each of the connecting plates.
In both the first and second double-headed mass sensors, there is preferably adopted the structure in which the direction of the extension of the center line equally dividing the plane surface of the first sensing plate and perpendicular to the joining direction of the first sensing plate and each of the connecting plates is parallel to the joining direction of the first connecting plate and said first diaphragm, and the joining direction of the second connecting plate and the second diaphragm, and the resonating portion has a shape symmetrical about the center line. When the double-headed mass sensor is immersed in electrically conductive solution in use, an each diaphragm is immersed in the electrically conductive solution. In order that the main element or subsidiary element is not immersed in the electrically conductive solution, it is preferable to provide a position sensor consisting of a pair of electrodes on said sensor substrate at the central position between each of said diaphragms and said main element.
Furthermore, according to the present invention, there is provided as a third double-headed mass sensor, a double-headed mass sensor characterized in that a side of each diaphragm is joined to a side of each connecting plate so that a first diaphragm is sandwiched between a first connecting plate and a second connecting plate, and a second diaphragm is sandwiched between a third connecting plate and a fourth connecting plate; a first sensing plate is bridged across said first connecting plate and said third connecting plate, and a second sensing plate is bridged across said second connecting plate and said fourth connecting plate; and a resonating portion comprising the first connecting plate, the first diaphragm, the second connecting plate, the second diaphragm, the third connecting plate, the fourth connecting plate, the first sensing plate, the second sensing plate, and a main element provided on at least one plane surface of each of said sensing plates, is bridged across the gap between the sides of a sensor substrate facing to each other joining at least a part of the side of each of said connecting plates to the sides of the sensor substrate.
Here, the main element may preferably be split in the direction perpendicular to the joining direction of each of the sensing plates and each of the connecting plates.
Moreover, according to the present invention, there is provided as a fourth double-headed mass sensor, a double-headed mass sensor characterized in that a side of each diaphragm is joined to a side of each connecting plate so that the first diaphragm is sandwiched between a first connecting plate and a second connecting plate, and the second diaphragm is sandwiched between a third connecting plate and a fourth connecting plate; each of said connecting plates is joined at the respective sides so that said first connecting plate is positioned between a first sensing plate and a third sensing plate, said third connecting plate is positioned between said first sensing plate and a fourth sensing plate, said second connecting plate is positioned between a second sensing plate and a fifth sensing plate, and said fourth connecting plate is positioned between said second sensing plate and a sixth sensing plate; a resonating portion comprising the first connecting plate, the first diaphragm, the second connecting plate, the second diaphragm, the third connecting plate, the fourth connecting plate, the first sensing plate, the second sensing plate, the third sensing plate, the fourth sensing plate, the fifth sensing plate, the sixth sensing plate, main elements provided on at least a part of at least one plane surface of said first sensing plate and said second sensing plate, and/or subsidiary elements provided on at least a part of at least one plane surface of one or more of said third sensing plate, said fourth sensing plate, said fifth sensing plate, and said sixth sensing plate, is bridged across the gap between the sides of a sensor substrate facing to each other joining at least a part of the side of each of said connecting plates to the sides of the sensor substrate.
Here, it is also preferable that each of the main elements and/or each of the subsidiary elements are split in the direction perpendicular to the joining direction of each of the sensing plates and each of the connecting plates.
In the above third and fourth double-headed mass sensors, it is preferable that the center line equally dividing the plane surface of the first sensing plate and perpendicular to the joining direction of the first sensing plate to the first connecting plate and the third connecting plate coincides with the center line equally dividing the plane surface of the second sensing plate and perpendicular to the joining direction of the second sensing plate to the second connecting plate and the fourth connecting plate; the direction of the extension of the center line is parallel to the direction where the first connecting plate and the second connecting plate sandwich the first diaphragm, and the direction where the third connecting plate and the fourth connecting plate sandwich the second diaphragm; and the resonating portion is constituted to have a shape symmetrical about each of the center line, and the line orthogonal to the center line and passing through the centers of the first diaphragm and the second diaphragm.
Furthermore, in all of the first to fourth double-headed mass sensors, a piezoelectric element consisting of a first electrode, a second electrode, and a piezoelectric film is preferably used as each of the main elements and/or each of the subsidiary elements, and as the structure thereof, a laminated structure in which the piezoelectric film is sandwiched between the first electrode and the second electrode, or a structure in which a comb-shaped electrode consisting of the first electrode and the second electrode facing to each other on the plane surface of the piezoelectric film or between the piezoelectric film and a sensing plate on which the piezoelectric film is provided, or a structure in which the piezoelectric film is provided in the gap between the first electrode and the second electrode forming the comb-shaped electrode, is preferably adopted. When a subsidiary element is provided, it is preferable that the direction of polarization of the piezoelectric film in each of the main elements is opposite to the direction of polarization of the piezoelectric film in each of the subsidiary elements. As the material for the piezoelectric film, a material consisting mainly of lead zirconate, lead titanate, and lead magnesium niobate is preferably used. It is also preferable that the available electrode area of the piezoelectric element is adjusted by removing a part of the first electrode and/or the second electrode with laser processing or machining.
The term xe2x80x9cpiezoelectricxe2x80x9d used herein includes piezoelectricity and electrostrictivity, and for example, piezoelectric ceramics include electrostrictive ceramics.
Furthermore it is preferable that each of the diaphragms, each of the connecting plates, and each of the sensing plates form the same plane surface through joining to each other, and that each of the sensing plates is fitted in and joined to the concave portion formed by each of the connecting plates and the sensor substrate. For this purpose, it is preferable that each of the diaphragms, each of the connecting plates, and each of the sensing plates are integrally formed from a vibration plate, and the sensor substrate is integrally formed by laminating the vibration plate and a base plate.
In addition to the above, it is preferable that spring plates are joined on a plane surface in the same direction of each of the connecting plates, or on both plane surfaces of each of the connecting plates, and each of the spring plates is joined to the sensor substrate or a spring plate reinforcing member. Here, it is preferable for improving mechanical reliability and temperature properties that each of the spring plates is integrally formed with an intermediate plate which is integrally formed between the diaphragm and the base plate, or integrally formed with the spring plate reinforcing member integral with the diaphragm, and formed also integrally with each of the connecting plates, and that each of them is made to have a structure not adhered with adhesives or the like. Furthermore, when such spring plates are provided, the structure comprising a reinforcing plate adhered to each of the spring plates, and joined to the sensor substrate is also preferably adopted. Such a reinforcing plate is also preferably formed integrally with each of the spring plates and the sensor substrate.
Also, by applying a catching substance, which reacts only with a substance to be sensed and catches the substance to be sensed, to the surface of at least one of the first diaphragm and the second diaphragm, or to at least a part of the surface of the resonating portion, the mass sensor can be preferably used, for example, as an immunosensor. Here, if electrode leads electrically connected to each of the main elements and/or each of the subsidiary elements, and electrodes forming each of the main elements and/or each of the subsidiary elements are insulated by an insulation coating layer consisting of a resin or glass, the mass sensor can be used in an electrically conductive solution without hindrance. Further, as the insulation coating material, the resin is more preferable than glass, and in particular, a fluorocarbon resin or a silicone resin is suitably used. Moreover, it is preferable for minimizing noise such as external electromagnetic waves, that at least a part of the surface of the insulation coating layer is coated by a shield layer consisting of a conductive material.
Further, stabilized zirconia or partially stabilized zirconia is suitably used as a material for each of the sensor substrates, each of the diaphragms, each of the connecting plates, each of the sensing plates, each of the spring plates, and the spring plate reinforcing member and the reinforcing plate, and it is preferable that the shapes of any of each of the diaphragms, each of the connecting plates, each of the sensing plates, and each of the spring plates are dimensionally adjusted by trimming with laser processing or machining.
Next, according to the present invention, there is provided a method for sensing a mass with a double-headed mass sensor in which connecting plates are joined to each of two diaphragms at respective sides, and a sensing plate on which a main element or a subsidiary element is provided as required bridges between said connecting plates, or sandwiches said connecting plates, and at least a part of the side of said connecting plate is joined to a sensor substrate, characterized in measuring with said element the resonant frequency of the resonating portion of said double-headed mass sensor on the basis of at least either one of: the bending-mode oscillation(vibration) in which said diaphragm, making the face where said connecting plate is joined to said sensor substrate the fixed face, bends in the direction perpendicular to a vertical axis passing through the center of said fixed face vertically, and in the direction perpendicular to the plane surface of said diaphragm; the axial rotation-mode oscillation (vibration) in which said diaphragm makes rotational oscillation (vibration) around said vertical axis making said vertical axis the central axis; the xcex8-mode swing oscillation (vibration) in which said diaphragm makes pendulum-like oscillation (vibration) centered on said vertical axis in the direction perpendicular to the side of said diaphragm and also perpendicular to said vertical axis; or the xcfx86-mode swing oscillation (vibration) in which said diaphragm makes pendulum-like oscillation (vibration) centered on said vertical axis with the swing in the direction perpendicular to the side of said diaphragm and also perpendicular to said vertical axis accompanied by the swing in the direction parallel to the side of said diaphragm.
Such a method for sensing a mass with a double-headed mass sensor is preferably adopted as a method for sensing a mass using the first and second double-headed mass sensors described above.
Furthermore, according to the present invention, there is provided a method for sensing a mass with a double-headed mass sensor in which each of two diaphragms is joined so as to be sandwiched by connecting plates at respective sides, a sensing plate on which a main element or a subsidiary element is provided as required bridges between said connecting plates, or sandwiches said connecting plates, and at least a part of the side of said connecting plate is joined to the sides facing to each other across the gap (or space) in the sensor substrate, characterized in measuring with said element the resonant frequency of the resonating portion of said double-headed mass sensor on the basis of either one of: the axial rotation-mode oscillation (vibration) in which said diaphragm, making the face where said connecting plate is joined to said sensor substrate the fixed face, makes rotational oscillation (vibration) around said vertical axis passing through the center of said fixed face vertically while making said vertical axis the central axis; the xcex7-mode surface rotational oscillation (vibration) in which said diaphragm makes rotational oscillation (vibration) around the center of said diaphragm in the plane surface of said diaphragm; the xcfx86-mode swing oscillation (vibration) in which said diaphragm makes pendulum-like oscillation (vibration) centered on said vertical axis with the swing in the direction perpendicular to the side of said diaphragm and also perpendicular to said vertical axis accompanied by the swing in the direction parallel to the side of said diaphragm; or the monoaxial-mode reciprocal oscillation (vibration) in which said diaphragm oscillates (vibrates) reciprocally in the plane surface of said diaphragm in the direction orthogonal to said vertical axis.
Such a method for sensing a mass with a double-headed mass sensor is preferably adopted as a method for sensing a mass using the third and fourth double-headed mass sensors described above.
In the two methods for sensing a mass with a double-headed mass sensor, the method in which by obtaining difference between two resonant frequencies produced by the fact that the masses of one diaphragm and the connecting plate joined to the diaphragm do not change, and the masses of the other diaphragm and the connecting plate joined to the other diaphragm change, change in the masses of the other diaphragm and the connecting plate joined to the other diaphragm is sensed, is preferably adopted.
As described above, the double-headed mass sensor of the present invention has features that change in a minute mass occurring in the resonating portion can be known exactly and quickly from a concrete value of change in the resonant frequencies of the resonating portion, the measuring operation is easy, and the measuring accuracy is high.
In addition, the double-headed mass sensor can measure various physical values by placing it in the environment where resonance frequency of the resonating portion including the diaphragms is changed. For example, it can be employed in a thickness meter for vapor-deposited films and a dew indicator utilizing direct changes in the mass of a diaphragm; and a vacuum gauge, a viscosity meter, and a temperature sensor utilizing the environment in which the sensor is placed, such as the degree of vacuum, viscosity, or temperature; and especially, it can be preferably employed to detect the presence of a substance to be sensed and to measure the mass of the substance by applying a catching substance that reacts specifically with the substance to be sensed, such as microorganisms, chemical substances, or the like in specimens and utilizing changes in its mass.